The overall objective of this proposal is elucidation of the mechanism by which insulin increases the reabsorption of phosphate in the renal proximal tubule. Specifically we propose to determine if insulin increases phosphate reabsorption by increasing the transport of phosphate across the lumenal brush bordar membranes of the proximal tubule. At the level of the brush border, studies will be performed to determine if the effects of insulin on phosphate transport are dependent upon; 1) the action of parathyroid hormone, 2) the transport of calcium, sodium and/or glucose, and 3) the phosphorylation of brush border membrane proteins. In support of our observation on isolated brush border membranes, the effects of insulin on phosphate transport into whole cells of renal cortex and the effects of insulin on phosphate reabsorption in vivo will be examined. Such studies will also include investigations into the possible role of parathyriod hormone, calcium glucose and sodium transport, and membrane phosphorylations in mediating the action of insulin. These studies not only have fundamental implications concerning the mechanism of insulin action but also will provide information about the mechanism and regulation of phosphate reabsorption by the kidney.